1. Field of the Invention
The present invention relates to a power generation module including a fuel cell having an oxide solid electrolyte such as zirconia as an electrolyte for a fuel cell power generation system and more particularly to a power generation module including a planar solid electrolyte type fuel cell. The present invention also relates to a solid electrolyte type fuel cell power generation system including such a power generation module. Further, the present invention relates to a sealing device for use in such a power generation module.
2. Description of the Prior Art
Fuel cells having an oxide solid electrolyte such as zirconia as the electrolyte operate at high temperatures as high as, for example, 800.degree. to 1,000.degree. C. and, hence, exhibit high efficiencies of power generation and require no noble metal catalyst. Because of the electrolyte being solid, such a type of fuel cell requires no management of electrolytes that is indispensable in other types of fuel cells. As a result, oxide solid electrolyte fuel cells are easy to handle and are hoped to be a third generation fuel cell.
However, oxide solid electrolyte type fuel cells use ceramics as major components and hence, they are susceptible to thermal damages due to thermal stress. If the entire fuel cell of this type is to be fixed with a ceramic adhesive, or the like, in order to seal it against gases, thermal stress tends to occur, which makes it difficult to realize a practical fuel cell. This difficulty has been overcome by the provision of a cylindrical cell, which is free from problems of the occurrence of thermal stress and necessity of gas sealing. In some cases, operational tests with such a cylindrical fuel cell have been successful. However, the cylindrical fuel cell shows a relatively low power generation density per unit volume of the cell, and at present, there is no expectation that an economically advantageous fuel cell can be obtained. Accordingly, to increase power generation density, fuel cells must be of a planar type.
FIG. 1 is a horizontal cross sectional view showing a conventional planar type solid electrolyte fuel cell as described in U.S. Pat. No. 4,910,100, and FIG. 2 is a vertical cross sectional view of the conventional planar type solid electrolyte fuel cell taken along the line II--II in FIG. 1. As shown in FIGS. 1 and 2, a cell stack 1 includes a plurality of single cells 2 and a plurality of separator plates 3, alternately built up one on another. Separator plates 3A are provided on the top and bottom of the stack 1, respectively. An oxidant gas supply manifold 4 and a fuel gas supply manifold 5 are provided in the central area of the cell stack 1. A plurality of guide vanes 6 are provided concentrically around the central area. Reactant gases, i.e., an oxidant gas and a fuel gas, are supplied from the oxidant gas supply manifold 4 and the fuel gas supply manifold 5, respectively, and directed by the guide vanes 6 to circumferential portions of the cell stack 1. The reactant gases are burnt in the outer periphery of the cell stack and introduced to a heat exchanger (not shown) through a pipe (not shown).
However, in the aforementioned conventional fuel cell, the exhaust fuel gas and the exhaust oxidant gas in the outer periphery of the cell stacks are mixed with each other and burnt at once. This results in an extraordinary increase in the temperature of the cell stack, and hence, it becomes difficult to stably run the fuel cell. This problem becomes much more severe especially when a plurality of stacks are arranged. Another problem involved is that metal pipes, conductors and the like are readily oxidized in an oxidative atmosphere at a high temperature and the service life of the fuel cell decreases accordingly. If the pipe used to conduct generated heat to the heat exchanger is long, there arise not only a problem of heat loss but also a problem of shortened service life of the pipe.